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F16/36480/2010 NDUNG’U CHRIS KIMANGA
i FCE 590: QUALITY OF GREY WATER
UNIVERSITY OF NAIROBI
QUALITY OF GREY WATER
By NDUNGÚ CHRIS KIMANGA
F16/36480/2010
A project report submitted as a partial fulfillment of the requirement for
the award of the degree of
BACHELOR OF SCIENCE IN CIVIL ENGINEERING
2015
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ABSTRACT
Numerous settlement areas around urban and rural areas are plagued by lack of a
public sewer system. Hence, septic tanks are installed in which the wastewater is
discharged.
When the septic tank gets full, vacuum trucks are hired to empty it. However, this
becomes expensive if done frequently.
A good solution to avoid high maintenance costs for septic tanks, would be to separate
grey water from black water. The black water can be led into the septic tank.
The grey water can undergo primary treatment systems such as filtration and settling
tanks, disinfection and constructed wetlands. From here, this water can be re-used or
discharged into the environment through soak pits depending on the effluent quality.
Waste water from households include black water (discharge from toilets) and grey
water (discharge from kitchens and bathrooms). Grey water however constitutes the
greater proportion of total wastewater. Grey water makes up about 50-80% of total
wastewater.
Samples were collected from a block of flats in Ongata Rongai and the quality of the
grey water would then determine the manner in which the effluent would be handled.
The study begins with the introduction and objectives and the literature review
together with the theoretical frame work highlighted. The methodology, data
collected, results and analysis are discussed within. Finally, the conclusions and
relevant recommendations are made.
The findings of the project are compiled in this report.
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DEDICATION
This project is dedicated to my parents. Your support is incomparable.
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ACKNOWLEDGEMENTS
This project completion has been made possible with the assistance of a number of people to
whom I would like to express my sincere gratitude.
I am indebted to my supervisors Eng. J N. Gitonga for his continued guidance, suggestions,
comments and encouragement throughout the period and completion of this study.
I would also like to express my gratitude to the Public Health Engineering Laboratory staff
for the assistance they gave me during the study.
Finally, I owe special thanks to my family for their encouragement and moral support.
Thank you all for your prayers.
MAY GOD BLESS YOU ALL
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1 CONTENTS
ABSTRACT ................................................................................................................................................ ii
DEDICATION ........................................................................................................................................... iii
ACKNOWLEDGEMENTS .......................................................................................................................... iv
LIST OF TABLES ...................................................................................................................................... vii
LIST OF MAPS ....................................................................................................................................... viii
LIST OF PLATES ....................................................................................................................................... ix
1 INTRODUCTION ............................................................................................................................... 1
1.1 BACKGROUND INFORMATION ................................................................................................ 1
1.2 PROBLEM STATEMENT ............................................................................................................ 1
1.3 STUDY OBJECTIVES .................................................................................................................. 2
1.4 SCOPE OF STUDY ..................................................................................................................... 2
2. LITERATURE REVIEW ....................................................................................................................... 3
2.1 INTRODUCTION TO GREY WATER ........................................................................................... 3
2.2 GREY WATER CHARACTERISTICS ............................................................................................. 3
2.3 GREY WATER REUSE ................................................................................................................ 5
2.3.1 BENEFITS OF GREY WATER REUSE .................................................................................. 5
2.3.2 USES OF RECYCLED GREY WATER ................................................................................... 6
2.3.3 UNTREATED GREY WATER .............................................................................................. 6
2.4 GREY WATER TREATMENT ...................................................................................................... 7
2.4.1 TREATING GREY WATER .................................................................................................. 7
2.4.2 GREY WATER TREATMENT SYSTEMS .............................................................................. 7
2.5 WATER QUALITY .................................................................................................................... 10
2.5.1 CHARACTERISTICS OF WATER ....................................................................................... 10
2.5.2 BACTERIOLOGICAL QUALITY OF WATER ....................................................................... 22
2.5.3 INDICATOR ORGANISMS ............................................................................................... 22
2.5.4 THERMOTOLERANT COLIFORM BACTERIA ................................................................... 23
2.6 BACTERIOLOGICAL QUALITY METHODOLOGIES ................................................................... 25
2.7 PUBLIC HEALTH CONSIDERATIONS ....................................................................................... 26
2.8 ENVIRONMENTAL CONSIDERATIONS.................................................................................... 28
3 METHODOLOGY ............................................................................................................................ 32
3.1 INTRODUCTION ..................................................................................................................... 32
3.2 BACKGROUND KNOWLEDGE OF THE STUDY AREA ............................................................... 32
.............................................................................................................................................................. 32
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3.2.1 LOCATION .................................................................................................................. 33
3.2.2 PLANNING AND URBAN DEVELOPMENT ........................................................... 33
3.2.3 GEOGRAPHY AND ECONOMY ............................................................................... 34
3.2.4 INFRASTRUCTURE ................................................................................................... 34
3.3 METHOD OF STUDY ............................................................................................................... 35
3.3.1 SAMPLING ..................................................................................................................... 35
3.3.2 LABORATORY TESTS. ..................................................................................................... 40
4 RESULTS AND ANALYSIS ................................................................................................................ 50
4.1 1st SAMPLE (FROM MANHOLE) ............................................................................................. 50
4.1.1 LAB RESULTS.................................................................................................................. 50
4.2 2nd SAMPLE (FROM PIPE) ...................................................................................................... 53
4.2.1 LAB RESULTS.................................................................................................................. 53
5 DISCUSSIONS ................................................................................................................................. 58
5.1 LAB RESULTS ......................................................................................................................... 58
5.1.1 SAMPLE 1 (FROM MANHOLE) ....................................................................................... 58
5.1.2 SAMPLE 2 (FROM PIPE) ................................................................................................. 58
5.2 POLLUTION LEVELS OF SAMPLES .......................................................................................... 59
5.3 REMARKS ON POLLUTION LEVELS ......................................................................................... 59
5.3.1 SAMPLE 1 ...................................................................................................................... 59
5.3.2 SAMPLE 2 ...................................................................................................................... 60
5.4 HOW TO HANDLE GREY WATER ............................................................................................ 60
5.4.1 DIVERT TO SEPTIC TANK ................................................................................................ 60
5.4.2 FILTRATION AND SETTLING SYSTEM ............................................................................. 61
5.4.3 USE OF SOAK PIT ........................................................................................................... 61
5.4.4 USE OF WETLANDS ........................................................................................................ 62
5.4.5 DISINFECTION ................................................................................................................ 62
6 CONCLUSION ................................................................................................................................. 64
7 RECOMMENDATIONS.................................................................................................................... 65
8 APPENDIX ...................................................................................................................................... 66
8.1 PHOTO GALLERY .................................................................................................................... 67
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LIST OF TABLES
Table 2.1: Various Sources Of Odour And Taste In Water 13
Table 2.2: Bacterial Waterborne Diseases 20
Table 2.3: Protozoa Waterborne Diseases. 20
Table 2.4: Standards For Effluent Discharge Into The Environment 29
Table 4.1: General Coliforms Lab Results (Sample 1) 49
Table 4.2: E. Coli Lab Results (Sample 1) 49
Table 4.3: COD Lab Results (Sample 1) 49
Table 4.4: BOD0 (Sample 1) 50
Table 4.5: BOD5 (Sample 1) 50
Table 4.6: Calculation of BOD (Sample 1) 51
Table 4.7: General Coliforms Lab Results (Sample 2) 53
Table 4.8: E. Coli Lab Results (Sample 2) 53
Table 4.9: COD Lab Results (Sample 2) 54
Table 4.10: BOD0 (Sample 2) 55
Table 4.11: BOD5 (Sample 2) 55
Table 4.12: Calculation of BOD (Sample 2) 55
Table 5.1: Lab Results 58
Table 5.3: Comparison of Sample Pollution Levels Against WQ Regulations 59
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LIST OF MAPS
MAP 1: THE SATELLITE IMAGE OF THE AREA OF STUDY 30
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LIST OF PLATES
Plate 3-1: Sampling Point: Block Of Apartments 31
Plate 3-2: Access Manhole, Sampling Point 1. 34
Plate 3-3: Obtaining the Sample 1 A) 35
Plate 3-4: Obtaining the Sample 1 B) 35
Plate 3-5: The Sample 1 Collected. 36
Plate 3-6: Pipe, Sampling Point 2. 37
Plate 3-7: The Sample 2 Collected. 37
Plate 3-8: PHE Laboratory. 38
Plate 4-1: Sample 1:300 Fully Depleted Of Dissolved Oxygen 51
Plate 8-1: Presumptive Test Reagents 66
Plate 8-2: BOD Test Bottles 66
Plate 8-3: Positive Presumptive Test Results 67
Plate 8-4: PH Meter 67
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1 INTRODUCTION
1.1 BACKGROUND INFORMATION
Grey water is composed of variable quantities of components of wastewater which may come
from the shower, bath tub, spa bath, hand basin, laundry tub, clothes washing machine,
kitchen sink and dishwasher.
Grey water therefore does not come from a toilet or urinal. Grey water contains impurities
and micro-organisms derived from household and personal cleaning activities. Because of the
high potential of grey water to contain pathogenic micro-organisms and other materials, it is
considered by health authorities to be a potentially infectious and polluting liquid waste
material which people normally want to eliminate from their homes. It is an accepted practice
and community expectation in sewered areas that grey water is drained to a sewer to promote
sanitation and hygiene in the home.
However, in non-sewered areas various on-site waste disposal systems need to be employed.
1.2 PROBLEM STATEMENT
In areas where there is no public sewer, people have installed septic tanks in which they
discharge their wastewater. When the septic tanks get filled up, residents acquire services
from private firms who empty the faecal sludge into vacuum trucks. Acquiring these services
are is costly.
So as to reduce the frequency of emptying these septic tanks, people opt to channel their grey
water and black water separately. In doing this, black water is channelled into the septic tanks
and grey water is channelled into a soak pit where the water seeps into the ground.
This reduces the cost significantly as proportion of grey water to the total waste water
produced from households is estimated to be about 60%. This practise saves money and
resources whereby only highly polluted wastewater is treated.
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However, in order to discharge wastewater into the environment, some parameters have to be
met to ensure this wastewater does not pollute the environment. This grey water has to be
analysed to ensure its quality is safe for discharge into the environment.
If the quality of the grey water is within the set parameters for discharge into the
environment, this practise can be encouraged amongst residents in areas which lack a pubic
sewer.
1.3 STUDY OBJECTIVES
The study was carried out through the following objectives.
- Determine the quality of grey water.
- Hence, determine a suitable on-site waste disposal system for areas with no public
sewers.
- Recommending solutions to improve on site disposal systems.
1.4 SCOPE OF STUDY
The study will focus on a block of apartments in Ongata Rongai and will involve.
Collecting grey water samples from the area of study
Conducting laboratory tests on the grey water samples
Tabulating and analysing the laboratory results.
Compare grey water quality against set effluent standards.
Suggest appropriate recommendations
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2. LITERATURE REVIEW
2.1 INTRODUCTION TO GREY WATER
Good quality drinking water in many areas is becoming a scarce commodity. Additional
demands is placed on limited water supplies as populations increase and there may be little
scope to expand available water sources, particularly for large cities e.g. Nairobi.
Grey water is defined as waste water generated from wash hand basins, showers and baths.
Grey water often includes discharge from laundry, dishwashers, kitchen sinks and other
domestic purposes.
This is unlike the discharge from toilets which is sewage or black water. It is called so (black
water) because it contains human waste.
The main difference therefore between grey water and sewage (black water) is, sewage has a
much larger organic loading as compared to grey water.
Grey water makes up the largest proportion of the total wastewater flow from households in
terms of volume.
Typically, 50-80% of the household wastewater is grey water. If a composting toilet is also
used, then 100% of the household wastewater is grey water. [(WHO). 2006. Guidelines for
the Safe Use of Wastewater.]
2.2 GREY WATER CHARACTERISTICS
Grey water characteristics vary according to:
1 The source: Be it a domestic household or office block.
2 Lifestyle characteristics of occupants
3 Water usage patterns.
The above are expounded further.
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2 The Source
The grey water that will be produced highly depends on the source.
Office block: Grey water would contain detergents for washing the floors and utensils. It will
contain less food particles concentration as compared to a domestic household where there is
relatively more cooking.
Domestic households: Grey water would contain relatively more solid particles from food,
dirt and lint as a result of cooking, cleaning and laundry activities respectively.
Factories: Grey water from factories might contain heavy metals or toxic chemicals which
will necessitate treatment of grey water before reuse. In addition, grey water from factories
may be very hot especially if used for cooling purposes. This hot water if discharged directly
into water bodies may will cause an imbalance of the aquatic environment hence putting the
aquatic organisms at risk of death.
Hospitals: Grey water from hospitals may contain a lot of chemicals and disease causing
micro-organisms. Hence, the reuse of grey water produced by hospitals is highly discouraged
as it will lead to illness and infections to anyone who comes into contact with this water.
For example, clothes worn by patients with highly contagious diseases are washed but the
grey water produced cannot be reused due to the risk of contracting the highly contagious
disease.
3 Lifestyle characteristics of occupants
Living standards: Occupants of an area with relatively higher income are more likely to use
more water hence will produce more grey water, other factors held constant. Occupants who
have relatively less income are more likely to conserve a lot of water where possible hence
their grey water discharge will be lower.
Single occupancies and Family occupancies: Single occupants are more likely to cook and
wash less hence the grey water composition will be different from family occupancies which
are more likely to cook and wash more.
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4 Water usage patterns
Grey water characteristics are dependent on the water usage patterns. This can be explained
as below
Early Mornings: A lot of people at this time will be taking a shower hence grey water
discharged in the morning have a large loading of hair, soaps and oils from bath tubs and
wash sinks.
Mid Mornings - Late Afternoon: At this time, a lot of people will do their laundry, house
cleaning and washing of kitchen utensils. The grey water produced will have a large loading
of lint, soil and food particles.
Early Evenings: Few people will take an evening shower hence grey water contains soaps,
oils and hair. A lot of food preparation goes on at this time hence food particles may be found
in the grey water.
2.3 GREY WATER REUSE
Most grey water is easier to recycle than black water, because of lower levels of
contaminants.
2.3.1 BENEFITS OF GREY WATER REUSE Grey water recycling has a lot of potential ecological benefits.
Lower fresh water extraction from rivers and aquifers: Reduced strain on the
natural resources brings about a more sustainable hydrological cycle.
Reduce strain on septic system or treatment plant - Grey water makes up the
majority of the household wastewater stream, so diverting it from the septic system
extends the life and capacity of the system. For municipal systems, decreased input
translates to more effective treatment at lower operational costs.
Groundwater Recharge - Grey water recycling for irrigation replenishes
groundwater.
Increased plant growth - Grey water used for irrigation can support plant growth in
areas that might otherwise not have enough water.
Reclamation of nutrients - The nutrients in the grey water are broken down by
bacteria in the soil and made available to plants hence improving soil fertility.
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Enhance water quality - Greater quality of surface and ground water when preserved
by the natural purification in the top layers of soil than generated water treatment
processes.
2.3.2 USES OF RECYCLED GREY WATER Grey water can be recycled for the following uses
1 Car washing
2 Irrigation
3 Toilet flushing
4 Construction
5 Fire fighting
Grey water contains solid particles (hair, lint, soil, food particles) which may however cause
land application systems to block.
Land applications system such as irrigation should have some type of coarse screens
installed. These systems will however require frequent maintenance and cleaning to ensure
no blockages occur.
2.3.3 UNTREATED GREY WATER
Untreated grey water should not be stored. This is because, untreated grey water when
stored will turn septic hence giving rise to bad odour and an environment for micro-
organisms to thrive.
However untreated grey water could still be put to good use.
However, the following precautions should be considered when using untreated grey
water
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a) Grey water containing sodium or bleaching agents can damage plants. For this reason,
such water should not be used for irrigation.
b) Grey water generated from kitchen sinks as a result of cleaning utensils may contain
grease, fats and oils and hence will be unsuitable for re-use.
2.4 GREY WATER TREATMENT
2.4.1 TREATING GREY WATER
This involves the improvement of the quality of grey water depending on the method of grey
water utilisation. Treatment systems consist of processes like settling of solids, floatation of
lighter materials, anaerobic digestion in a septic tank, aeration, clarification and finally
disinfection.
Treatment processes only reduce the gross primary pollutant nature of wastewater. Secondary
pollution may still occur because chemical components such as nitrates, phosphates and
sodium may not be reduced by treatment processes.
2.4.2 GREY WATER TREATMENT SYSTEMS
Some treatment processes include;
2.4.2.1 TANKS
Use of a settling tank enables solids and large particles to settle to the bottom, while grease,
oils and small particles will float. The remaining liquid will be reused. A settling tank also
allows for hot water to cool before reuse.
Such tanks should be large enough to hold twice the expected dally flow plus 40 % to allow
for sludge accumulation and surge loading. One widely-used type of settling tank well-suited
for grey water treatment is a septic tank.
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A septic tank is specifically designed to allow settling. The use of a septic tank to treat grey
water should never be confused with the conventional use of a septic tank. Grey water
intended for reuse should never be mixed with toilet wastes.
Grey water coming out of a septic tank contains very little or no oxygen. Grey water from an
aerobic tank will contain more oxygen, which is better for irrigation purposes. An electrical
pump or aerator could be added to a septic tank to create an aerobic environment. Aerobic
conditions allow more decomposition of wastes in the tank thus may help to minimize sludge
build-up and blockages in the system.
Both aerobic and septic tanks will need to be emptied from time to time depending on the
quantity of grey water generated into the tank. An interval of 5 years of emptying will suffice
to avoid backflow or leakages due to overflow.
2.4.2.2 DISINFECTION
The most common chemical used to disinfect water is chlorine. This is because it is cheap,
readily available, and stable and will, with time, vaporize from the water after disinfection.
Organic matter in grey water may combine with chlorine hence reducing the amount
available for the disinfection process. Because of this reason, a settling tank or filter before
this stage is highly recommended.
Iodine could also be used since it is less affected by organic material, persists longer and may
be more effective at high pH of grey water. However, it is not widely used as compared to
chlorine particularly in Kenya.
2.4.2.3 FILTERS
The type of filter required for a grey water system depends on the amount of grey water to be
filtered and the type of contaminants present. A drain filter is an easy and cheap way to filter
out lint, hair and food particles. A cloth bag can be tied at the end of a garden hose and this
will filter grey water during irrigation.
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Commercial water filters could also be used. Most households use an activated charcoal,
cellulose or ceramic cartridge that must be clean or replaced regularly. Slow sand filters may
also be used and these are built by the homeowner.
Slow sand filters require regular cleaning and replacement of the top layer of media.
Directing grey water to a settling tank before filtering reduces contaminant load and hence
lengthen the efficiency and life of the filtering media.
2.4.2.4 CONSTRUCTED WETLANDS
Physical, chemical, and biological processes are combined in wetlands to remove
contaminants from wastewater. Grey water treatment is achieved by soil filtration in reed-bed
systems which reduces the organic load of the grey water considerably
In addition, constructed wetlands decrease the concentration of faecal bacteria. If designed
properly, these systems would produce a clear and odourless effluent.
Constructed wetlands tend to be simple, cheap to maintain and environmentally friendly. On
top of that, they provide food for aquatic organisms and increase the aesthetic value in an
area by improving the appearance of the landscape.
2.4.2.5 ROTATING BIOLOGICAL CONTACTORS (RBC)
This is a biological treatment process used in the treatment of wastewater following primary
treatment. Primary treatment process removes the grit and other solids through a screening
process followed by a period of settlement.
The RBC process involves allowing the wastewater to come in contact with a biological
medium in order to remove contaminants in the grey water before discharge of the treated
grey water to the environment.
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It consists of a series of closely spaced, parallel discs mounted on a rotating shaft, whereby
microorganisms grow on the surface of the discs where the biological process of breaking
down the wastewater takes place.
2.4.2.6 MEMBRANE BIOREACTORS (MBR)
The membrane bioreactor is basically a suspended growth activated sludge system that
utilises micro-porous membranes for liquid separation. The system consists of a pre-treatment
settling tank, an aerated settling tank which also stores the intermittently produced grey water
and the aerated activated sludge tank.
The generated grey water is held back by the submerged membrane filter module installed in
the aeration tank. The purified grey water passes through the membrane yielding a bacteria-
free effluent.
2.5 WATER QUALITY
Water quality refers to the chemical, physical, biological and radiological characteristics of
water. The specific treatment process used in any specific case depends on the nature and
quality of the raw water and the desired water quality.
There are various references which can be used to assess the sufficiency of water treatment
but the International Standards for Drinking Water (WHO) in its revised forms and the
Kenyan adaptations of the same are probably the most suited in this country.
2.5.1 CHARACTERISTICS OF WATER
Water characteristics are divided into physical, chemical and biological characteristics.
2.5.1.1 PHYSICAL CHARACTERISTICS OF WATER
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a) Colour
Presence of colour in water is due to substances in solution or in colloidal suspension, which
can be unacceptable especially in high levels. Colour could also be due to extraction of
colouring materials from humus or any other organic matter.
Experience shows that consumers may turn to alternative, perhaps unsafe sources when their
water displays aesthetically displeasing levels of colour.
The guideline value is 15 True Colour Units (TCU). This is the WHO guideline. Most people
can detect levels of colour above 15 TCU in a glass of water. (Tebbutt, 1983)
b) Temperature
Temperature change impacts chemical and biological characteristic of surface water.
Temperature also affects the dissolved oxygen (DO) levels in water, photosynthesis of
aquatic plants and metabolic rates of aquatic organisms.
Thermal pollution occurs when relatively warmer water is introduced into a water body.
Sources of warm water mostly include industries where water is used for cooling purposes.
c) Turbidity
Turbidity is defined as the dispersion and interference of light passage due to the presence of
suspended particles.
Some of the causes of turbidity include, surface runoff, algae growth and discharge from
waste. Surface water is more prone to experiencing turbidity especially during the rainy
seasons.
Suspended particles in turbid water absorb heat from sunlight, making it warmer hence
reducing concentration of DO in the water. This poses a risk to survival of some aquatic
organisms.
The main impact of turbidity lies in its aesthetic value in that highly turbid water is an
indicator of the bad quality of the water. Turbidity is measured in NTU Nephelometric
Turbidity Units, measured by a turbidimeter or nephelometer. WHO standards state that
maximum allowable turbidity in drinking water should not be more than 5NTU.
Turbidity in excess of 5NTU may be noticeable and consequently objectionable to
consumers.
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d) Solids
Solids in water are categorised into 2 main classes
- Total dissolved solids (TDS)
- Total Suspended solids (TSS)
Total dissolved solids are a measure of all inorganic and organic substances contained in a
liquid in molecular, ionized or micro-granular suspended form.
Total suspended solids include all particles in water which will not pass through a filter.
Settleable solids are those that can settle out in a graduated hope cone and can be measured
volumetrically.
e) Electrical conductivity
Electrical conductivity is the ability of a substance to conduct an electrical current, measured
in microsiemens per centimetre (mS/cm). Electrical conductivity of water depends on the
quantity of dissolved salts present and for a dilute solution, it is proportional to total dissolved
solids content (TDS).
Hence, conductivity is often used to estimate the amount of total dissolved solids (TDS)
rather than measuring each constituent separately.
The relationship between conductivity and TDS can hence be expressed using the following
equation
Conductivity = K. TDS
K = constant
f) Taste and Odour
Water for domestic use should have no taste or odour. Tastes and odours may be due to the
presence of organic substances for example algae growth and decomposing matter. In
addition, domestic, industrial and agricultural activities may also cause tastes and odours.
Changes in normal taste of a public water supply may signal changes in the quality of the
water source of poor treatment practices.
Generally, the taste buds in the oral cavity detect the inorganic compounds of metals such as
magnesium, calcium, sodium, copper, iron and zinc. (WHO
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Table 2.1: VARIOUS SOURCES OF ODOUR AND TASTE IN WATER.
TASTE OR ODOR SOURCE
Musty MIB, isopropylmethoxypyrazine
(IPMP), isobutylmethoxypyrazine
(IBMP)
Turpentine, oily Methyl tertiary butyl ether (MTBE)
Fishy/rancid 2,4-heptadienal,octanal
Chlorinous Chlorine
Medicinal Chlorophenols, iodoform
Oily, gas-like, paint Hydrocarbons, volatile organic compounds
(VOCs)
Metallic Iron, copper, zinc, manganese
Grassy Green algae
Earthy Geosmin
Source: (Trojan technologies, 2005)
2.5.1.2 CHEMICAL CHARACTERISTICS OF WATER
Chemical properties of surface water depends on the characteristics of the catchments or
source.
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These chemical properties include:
a) PH
PH is a measure of the intensity of acidity or alkalinity of water. Measurement is carried out
on a pH scale from 0 to 14 with 7 as the neutral. When the pH value is less than 7, it is acidic
and when the value is above 7, it is alkaline.
Water in its natural state is ionized to hydroxyl and hydrogen ions as shown below.
H2O ⇌ H+ + OH-
PH is given by
PH= -log10 = log10 (1/ [H+])
Many chemical reactions are controlled by pH and biological activity is usually restricted to a
fairly narrow pH range of 5 to 8. Highly acidic or alkaline water is undesirable because of
corrosion hazards and possible difficulties in treatment.
b) Dissolved oxygen
Dissolved oxygen is an important element in water quality control. Dissolved oxygen
concentration is determined by the physical (temperature and pressure), chemical (presence
of reducing and organic substances) and biochemical (microorganisms and biodegradable
substances) activities prevailing in the water body.
Presence of dissolved oxygen in water is essential to sustain the higher forms of biological
life and the oxygen balance of the system largely determines the effect of wastewater
discharge into a river.
Adequate dissolved oxygen is necessary for good water quality
As dissolved oxygen levels in water drop below 5.0mg/l, aquatic life is put under stress. The
lower the concentration the greater the stress. (KY Water watch, 2013)
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c) Biochemical Oxygen Demand
Biochemical Oxygen Demand (BOD) is defined as the amount of oxygen required by
bacteria while breaking down decomposable organic matter under aerobic conditions. The
BOD test is an empirical bioassay-type procedure which measures the dissolved oxygen
consumed by bacteria (and other microbial life) while the organic substances present in the
solution.
The BOD standard test conditions are incubation at 20℃ in the dark for a specified period
time, mostly five days. The reduction in dissolved oxygen concentration during this
incubation period is a measure of the biochemical oxygen demand and is expressed in mg/l
oxygen or mg/l BOD.
The BOD test is widely used to determine the “pollutional strength” of domestic and
industrial wastes in terms of the oxygen that they will require after being discharged into
natural waters systems.
A high BOD value hence means that the wastewater will require a large quantity of oxygen
from the surrounding natural waste system. Hence, a very high BOD value is detrimental to
aquatic life as it will lead to depletion levels in oxygen levels.
d) Chemical Oxygen Demand
The chemical oxygen demand (COD) test is a measure of the quantity of oxygen required to
oxidise the organic matter in a waste water sample, under specific conditions of oxidising
agent, temperature and time.
During the determination of COD, organic matter is converted to carbon dioxide and water,
amino nitrogen to ammonia nitrogen and organic nitrogen in higher oxidation states to
nitrates regardless of the biological degradability of the substances. For example glucose
(biologically degradable) and lignin (biologically resistant) are both oxidised completely.
As a result, COD values should be greater than BOD values and may be much greater when
significant amounts of biologically resistant organic matter is present.
COD values are used extensively in the analysis of industrial wastes. In conjunction with the
BOD test, the COD test is helpful in indicating toxic conditions and the presence of
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biologically resistant organic substances. The test is widely used in the operation of treatment
facilities because of the speed with which results can be obtained.
e) Chloride
Excess chloride of about 250 mg/litre in water leaves a bad taste in water. In addition, excess
chloride ions (Cl-) ions in water may result to water hardness.
Chloride concentrations exist in natural waters as observed in sea water. Wastewater also
contains large amounts of chloride, as do some industrial effluents. Chlorides are widely
distributed in nature as salts of sodium (NaCl), potassium (KCl) and calcium (CaCl2).
Chlorides are leached from various rocks into water by weathering. The chloride ion is highly
mobile and is transported to closed basins or oceans.
Chlorides also increases the electrical conductivity of water and thus increases its corrosivity.
f) Carbon (IV) oxide
Carbon (IV) oxide in water exists in form of carbonates, or as free carbon (IV) oxide. When
carbon (IV) oxide dissolves in water, it forms carbonic acid which is corrosive hence will
destroy steel pipes in the distribution system. High levels of carbonates tend to cause lime
scale deposits which with time reduces the useful cross-sectional area of pipes.
g) Hardness
Water hardness is a characteristic that prevents lather formation from soap. Hardness is a
measure of water to consume soap without the formation of lather. It is mainly caused by the
cations, calcium and magnesium in combination with anions, carbonate, chloride and
sulphate.
Hard drinking water is generally not harmful to one’s health, but can pose serious problems
in industrial settings, where water hardness is monitored to avoid costly breakdowns in
boilers, cooling towers and other equipment that handle water.
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Other problems associated with hard water include grey staining of washed clothes, scum on
wash basins following use of soap and reduced water flow in hot water distribution pipes due
to scale build-up.
The most common method of removing hardness from drinking water is the installation of
water softener. A water softener replaces the calcium and magnesium molecules with sodium
molecules. However, high levels of sodium in drinking water will have an adverse effect on
the health of the consumer. Persons on a sodium restricted diet or suffering from high blood
pressure are not allowed to drink water with more than 20mg/l of sodium (Vermont
Department of Health, 2013)
h) Alkalinity
Alkalinity is the measure of the ability of water to absorb hydrogen ions which are almost
entirely due to hydroxide, bicarbonate and carbonate ions in the reaction.
OH- + H
+⟷H2O
CO32-
+ H+ ⟷
HCO3-
HCO3- + H
+⟷ H2CO3
Most of the alkalinity in raw water is due to the presence of bicarbonate ions produced by the
action of ground water on limestone or chalk.
Alkalinity has no health significance but is very important for the water treatment processes
particularly coagulation/flocculation and chlorination. In addition, Alkalinity is useful in
water in the sense that it provides buttering to resist the changes in PH.
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i) Acidity
Acidity arises from the presence of weak or strong acids and/or certain inorganic salts. The
presence of dissolved carbon (IV) oxide is usually the main acidity factor in unpolluted
surface waters. Carbon (IV) oxide dissolves in water to form weak carbonic acid (H2CO3).
Acidity has no health and sanitary implications apart from palatability considerations in
excessively acid waters.
High acidity in water causes corrosion in distribution pipes.
j) Iron and Manganese
Iron makes up at least 5% of the earth’s crust. Rainwater infiltrates the soil and underlying
geological formations dissolving iron as it seeps into aquifers that serve as sources of ground
water for wells.
Presence of large iron concentration in public water supplies causes staining in plumbing
fixtures and washed clothes. Iron can cause water hardness though to a lesser extent as
compared to magnesium and calcium ions.
WHO water quality standards for public water supplies state the maximum allowable Iron
concentration to be 0.3 mg/l.
Manganese behaves so much like iron that it is sometimes difficult to distinguish the two.
This s in that, excess quantities of manganese leads to staining of washed clothes and small
quantities affect water colour.
WHO water quality standards for public water supplies state the maximum allowable
manganese concentration to be 0.1 mg/l.
2.5.1.3 BIOLOGICAL CHARACTERISTICS OF WATER
Disease carrying microorganisms can be carried in water and their presence in drinking water
is a serious hazard to human health. Such microorganisms that cause disease by transmission
through contaminated water are called waterborne pathogens.
a) Microbiology
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Microbiology is the study of microorganisms, of small living things. Microorganisms of
interest to the water quality include the following:
- Bacteria
- Protozoa
- Viruses
- Algae
- Fungi
Bacteria
These are primitive, single-celled organisms with a variety of shapes. Bacteria range in size
from 0.5 to 2 microns in diameter and about 1 to 10 microns in length. Bacteria are
categorised into 3 general groups based on the physical shape.
Rod-shaped bacteria are called bacilli
Spherical shape bacteria are called cocci
Spiral-shaped bacteria
Bacteria are responsible for a number of diseases. The bacterial pathogen responsible for
these diseases enter potential drinking water supplies through faecal contamination. The table
below shows a number of bacterial waterborne diseases.
Table 2.2: BACTERIAL WATERBORNE DISEASES.
Bacteria Disease
Salmonella typhi Typhoid fever
Shigella spp. Gastroenteritis
Vibrio cholera Cholera
Campylobacter spp. Gastroenteritis
Enteropathogenic E. coli Gastroenteritis
Leptospira spp. Leptospirosis
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Protozoa
Protozoa are one-celled animal like organisms with a fairly complex cellular structure. The
protozoa are the giants of the microbial world. They are many times larger than bacteria and
range in size from 4 to 500 microns.
They are categorized into the following groups based on their method of locomotion.
• Amoebas: move about by a gliding action. Have changing shape as they glide from
place to place.
• Ciliates: covered with short hair-like projections called cilia, which beat rapidly and
propel the ciliates through the water.
• Flagellates: have one or more long whip-like projections, called flagella, which propel
the free-swimming organisms.
• Suctoria: these are attached organisms, similar to attached ciliates, but have tentacles
rather than cilia.
• Sporozoa: they are non-mobile and are simply swept along with the current of the
water.
Protozoa are responsible for the following waterborne diseases.
Table 2.3: PROTOZOA WATERBORNE DISEASES.
Protozoa Disease
Entamoeba histolytica Amoebic dysentery
Glardia lamblia Glardiasis
Cryptosporidia Cryptosporidosis
Viruses
They are many times smaller than the bacteria. Range in size from 0.02 to 0.25 microns in
diameter. Viruses are intra-cellular parasites that must have a host cell in which to multiply.
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They are extremely simple life forms. They contain no mechanisms by which to obtain
energy or reproduce some of their own.
Waterborne diseases caused by bacteria include
- Hepatitis
- Viral gastroenteritis
- Poliomyelitis
Algae
Algae are a form of aquatic plants. Although in mass, they are easily seen by the naked eye,
many of them are microscopic as single cells. They exist as single-celled forms and also as
huge, multicellular forms, such as marine kelp. They occur in fresh and polluted water, as
well as in salt water.
They are able to use energy from the sun though photosynthesis. They usually grow near the
surface of the water because light cannot penetrate very deep through the water.
Algae are categorised in the following groups based on their colour:
• Green algae: contain green chlorophyll and are found mostly in fresh water. This form
is the green roadside ditch algae, and the type that grows on clarifier and basin walls.
• Eugleniods: single-celled, green pigmented algae that resemble protozoa. They have
flagella, but are considered algae because they carry out photosynthesis.
• Diatoms: are golden-brown, single celled forms that have a hard silica shell. The
shells of millions of dead diatoms are mined commercially and known as
diatomaceous earth.
• Blue-green algae: is bluish-green in colour and undergoes photosynthesis.
Although algae are not considered waterborne pathogens, they do cause some problems with
water operations. They grow easily on walls of basins and troughs, and heavy growth may
cause plugging of screens and intakes. Algae also releases chemicals that can cause taste and
odour problems in drinking water.
Control of algae in raw water supplies is done with chlorine and potassium permanganate.
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Fungi
Fungi are non-photosynthetic organisms that grow as multicellular, filamentous, mould-like
forms or as single-celled, yeast-like organisms. Fungi must have organic material as a food
source.
2.5.2 BACTERIOLOGICAL QUALITY OF WATER
The principal risk associated with water in community supplies is that of infectious diseases
related to faecal contamination.
The microbiological examination of drinking water emphasizes assessment of the hygienic
quality of the supply. This requires the isolation and enumeration of organisms that indicate
the presence of faecal contamination
In certain circumstances, the same indicator organisms may also be used to assess the
efficiency of drinking water treatment plants, which is an important element of quality
control. Other microbiological indicators, not necessarily associated with faecal pollution,
may also be used for this purpose.
2.5.3 INDICATOR ORGANISMS
The US Environmental Protection Agency (EPA) lists the following criteria for an
organism to be an ideal indicator of faecal contamination
1. The organism should be present whenever pathogens are present.
2. The organism should be useful for all types of water.
3. The organism should have a longer survival time than the hardiest pathogen.
4. The organism should be found in warm-blooded animals’ intestines.
Examples of indicator organisms include:
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2.5.4 THERMOTOLERANT COLIFORM BACTERIA
These are the coliform organisms that are able to ferment lactose at a temperature of 44 –
45℃.This group includes the genus Escherichia and some species of Klebsiella, Enterobacter
and Citrobacter.
Regrowth of the bacteria in the distribution system is unlikely unless sufficient bacterial
nutrients are present, unsuitable materials are in contact with the water or the water is above
13℃, and there is no free residual chlorine.
Mostly, presence of thermotolerant coliform is directly related to that of E. coli. Its use for
assessing water quality is hence acceptable for routine purposes. Thermotolerant coliform
organisms are readily detected, therefore play an important secondary role as indicators of the
presence of faecal bacteria in water.
Thus, thermotolerant coliform organisms may be used in assessing degree of treatment
necessary for waters of different quality and for defining performance targets for removal of
bacteria.
2.5.4.1 COLIFORM ORGANISMS (TOTAL COLIFORMS)
Coliform organisms have been widely used as a suitable microbial indicator of water quality,
largely because they are easy to detect in water. The term “coliform organisms” refers to
Gram-negative, rod-shaped bacteria capable of growth in the presence of bile salts or other
surface-active agents with similar growth-inhibiting properties and able to ferment lactose at
35–37°C with the production of acid, gas, and aldehyde within 24–48 hours.
Presence of coliform organisms however do not always directly relate to the presence of
faecal contamination or pathogen in water, however, this test is useful for monitoring the
microbial quality of water.
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2.5.4.2 FAECAL STREPTOCOCCI
This is streptococci generally present in human and animal faeces. Faecal streptococci rarely
multiply in polluted water, and they are more persistent than E. coli and coliform bacteria.
They are therefore valuable as indicators of water quality.
In addition, faecal streptococci are highly resistant to drying and therefore will be valuable
for routine checks on distribution systems or for detecting pollution of ground waters or
surface waters by surface run-off.
2.5.4.3 ESCHERICHIA COLI (E. COLI)
Escherichia coli is a member of the family Enterobacteriaceae. Escherichia coli is abundant
in human beings and animal faeces. E. coli is a species of faecal coliform bacteria that is
specific to faecal material from humans and other warm-blooded animals. EPA recommends
E. coli as the best indicator of health risk as it is used as an indicator to monitor the possible
presence of other more harmful microbes.
It is found in sewage, treated effluents and natural waters and soils which have been subject
to faecal contamination, whether from humans, wild animals, or agricultural activity.
Presence of E. coli cannot be ignored because it brings to the conclusion that the water has
been faecally contaminated and hence the presence of pathogen in the water is possible.
Possible sources of faecal contamination include:
- Agricultural runoff
- Wildlife that uses the water as their natural habitat
- Runoff from areas contaminated with pet manure
- Wastewater treatment plants
- On-site septic systems
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2.6 BACTERIOLOGICAL QUALITY METHODOLOGIES
Plate Count Method: It is a relatively simple method used to find the concentration
of coliform in a sample of water. It involves the fixing single invincible cells in
position and creating favourable conditions. I.e. nutrients, temperature, pH and many
more to enable the cells to grow into colonies of millions of cells clustered together at
the spot where the cells are fixed so that one can count them. Knowing the volume of
water taken, one can then work out the density of the cells.
For best results the colonies should neither be overcrowded or too few. Hence dilution
may need to be applied. Coliforms are used to assess the effectiveness of disinfection.
Multiple tube: In this method, a measured sub-sample (perhaps 10ml) is diluted with
100 ml of sterile growth medium and an aliquot of 10 ml is then decanted into each of
ten tube is then decanted into each of ten tubes The remaining 10 ml is then diluted
again and the process repeated. At the end of 5 dilutions this produces 50 tubes
covering the dilution range of 1:10 through to 1:10000.
The tubes are then incubated at a pre-set temperature for a specified time and at the
end of the process the number of tubes with growth in is counted for each dilution.
Statistical tables are then used to derive the concentration of organisms in the original
sample. This method can be enhanced by using indicator medium which changes
colour when acid forming species are present and by including a tiny inverted tube
called a Durham tube in each sample tube. The Durham inverted tube catches any gas
produced. The production of gas at 37 degrees Celsius is a strong indication of the
presence of Escherichia coli.
Filter membrane: This is a refinement of total plate count in which serial dilutions of
the sample are vacuum filtered through purpose made membrane filters and these
filters are themselves laid on nutrient medium within sealed plates. This method is
otherwise similar to conventional total plate counts. Membranes have a printed
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millimetre grid printed on and can be reliably used to count the number of colonies
under a binocular microscope.
2.7 PUBLIC HEALTH CONSIDERATIONS
Grey water is contaminated with human and animal excretions from bathing, food
preparation and from washing clothes. All forms of grey water are therefore capable of
transmitting disease.
Disease transmission is principally through the faecal-oral route where the grey water may be
directly ingested through contaminated hands, or indirectly ingested through contact with
contaminated items such as grass, soil, toys, garden implements, and diversion or treatment
devices while they are being serviced.
Transmission may also occur through inhalation of irrigated spray, by penetration through
broken skin, by insect vectors such as flies and cockroaches and vermin vectors such as rats
and mice.
Even household pets may transmit disease by tracking and carrying grey water into the home
or when petted by children.
Ground water contamination and pollution may also lead to disease transmission.
Contaminated drinking water aquifers may facilitate ingestion of pathogens when the water is
used for drinking and other domestic purposes.
People vary in their susceptibility to disease while some people may pass pathogenic micro-
organisms without showing any symptoms of the disease. As the number of persons in a
community served by a centralised wastewater management facility increases so does the risk
of transmission. This is because the diversity (number of the types) of pathogenic micro-
organism load increases with the population.
The same applies to a community increasingly served by on-site wastewater management
systems such as grey water treatment devices. Such a risk to health should be recognised as a
cumulative impact of installation or development.
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Therefore, to reduce the risk of transmission, all reused grey water must be totally contained
within the boundaries of the premises. Care must be taken to ensure that there is no cross
connection between the grey water reuse system and the water supply so that drinking water
is not inadvertently contaminated. This has the greatest chance of occurring when grey water
is used for toilet flushing and a cross connection accidentally is made to the water supply.
Grey water reuse plumbing if used for toilet flushing should be coloured purple and labelled
“Treated wastewater – not fit for human consumption.” A backflow prevention device should
also be fitted to the water supply.
Where grey water reuse is practiced the sewer must still be available for reconnection or used
as an overflow during wet weather or when excess grey water cannot be utilised. During wet
weather untreated grey water may be brought to the surface as the water table rises and
therefore provide a source of contamination.
Caution must be exercised with the reuse of grey water to ensure that the potential to transmit
disease has been minimised. This is achieved by:
- Minimising human contact with untreated grey water i.e. subsurface utilisation
- Placing barriers between the grey water and people (and their pets) to minimise
exposure to grey water by containing grey water in vessels or tanks as it is utilised.
- Disinfection to an even higher standard for utilisation in toilet and urinal flushing or
laundry use.
- Sign posting the land application system to advise that grey water is being reused and
that contact must be avoided.
- No irrigation using grey water during periods of wet weather.
- Distinguishing plumbing which contains recycled grey water and to prevent cross
connection to the potable water supply.
- Maintaining a connection to the sewer so as to enable isolation of the land application
system.
- Installing a backflow prevention device on the potable water supply when grey water
is used for toilet flushing.
- Not irrigating raw or treated grey water on edible plants which are consumed raw.
- Using a dedicated land application system not used for recreation such as a children’s
play area or BBQ area.
- Not storing grey water except for surge attenuation, unless treated and disinfected;
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- Preventing surface ponding or surface run-off of grey water and confining grey water
within the disposal area.
2.8 ENVIRONMENTAL CONSIDERATIONS
To manage wastewater effectively it is essential that water conservation is practiced.
Wastewater generation should be minimised for three important reasons
- To conserve drinking water as a precious natural resource;
- To ensure that wastewater does not overload the installed grey water management
system, which may then cause a public health risk, as discussed in the preceding
chapter.
- To minimise land requirements for a grey water reuse system.
However, if mishandled, grey water could cause harm to the environment as discussed
below.
• By exceeding the hydraulic loading, the land application system with water
causing run off of polluted water to storm-water drains, rivers, streams and other
people’s property.
• By raising the water table which may affect foundations of houses causing
instability in structures.
• By causing the soil to become permanently saturated, it may prevent plants from
growing and cause odour.
• By altering the soil salinity.
• Altering the soil permeability.
• Changing the soil pH.
• Altering the soil electrical conductivity.
• By degrading the soil with chemical impurities which affect the properties of the
soil to assimilate nutrients or water.
Because grey water contains many impurities, including the nutrients of nitrogen and
phosphorus, which may harm the environment and the soil in particular, great care must be
exercised when designing land application areas to ensure that they are sustainable. There are
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some chemicals which are not capable of being treated or degraded in the soil. Therefore, the
soil ecosystem must be capable of adsorbing, absorbing, assimilating or treating the chemical
impurities and nutrients without medium term and long term degradation of the soil, or the
environment.
Domestic grey water treatment systems are designed primarily to treat organic matter and are
not normally designed to remove many chemical salts, such as sodium, nitrates and
phosphates, which may be found in grey water.
2.9 LEGISLATION
2.9.1 WATER QUALITY REGULATIONS
The Minister for Environment and Natural Resources in consultation with relevant lead
agencies made regulations. These regulations are known as the Environmental Management
and Coordination, (Water Quality) Regulations 2006.
The authority with the mandate to enforce these regulations is known as the National
Environment Management Authority established under section 7 of the Environmental
Management and Co-ordination Act No.8 of 1999.
NEMA ensures that effluent discharged into the environment like in our case (grey water into
soak pits) meets the following standards.
Table 2.4: STANDARDS FOR EFFLUENT DISCHARGE INTO THE
ENVIRONMENT
Parameter Max
Allowable(Limits)
1,1,1-trichloroethane (mg/l) 3
1,1,2-trichloethane (mg/l) 0.06
1,1-dichloroethylene 0.2
1,2-dichloroethane 0.04
1,3-dichloropropene (mg/l) 0.02
Alkyl Mercury compounds Nd
Ammonia, ammonium compounds, NO3 compounds
and NO2 compounds (Sum total of ammonia-N
times 4 plus nitrate-N and Nitrite-N) (mg/l)
100
Arsenic (mg/l) 0.02
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Arsenic and its compounds (mg/l) 0.1
Benzene (mg/l) 0.1
Biochemical Oxygen Demand (BOD 5days at 20 oC) (mg/l) 30
Boron (mg/l) 1.0
Boron and its compounds – non marine (mg/l) 10
Boron and its compounds –marine (mg/l) 30
Cadmium (mg/l) 0.01
Cadmium and its compounds (mg/l) 0.1
Carbon tetrachloride 0.02
Chemical Oxygen Demand (COD (mg/l) 50
Chromium VI (mg/l) 0.05
Chloride (mg/l) 250
Chlorine free residue 0.10
Chromium total 2
cis –1,2- dichloro ethylene 0.4
Copper (mg/l) 1.0
Dichloromethane (mg/l) 0.2
Dissolved iron (mg/l) 10
Dissolved Manganese(mg/l) 10
E.coli (Counts / 100 ml) Nil
Fluoride (mg/l) 1.5
Fluoride and its compounds (marine and non-marine) (mg/l) 8
Lead (mg/l) 0.01
Lead and its compounds (mg/l) 0.1
n-Hexane extracts (animal and vegetable fats) (mg/l) 30
n-Hexane extracts (mineral oil) (mg/l) 5
Oil and grease Nil
Organo-Phosphorus compounds (parathion,methyl parathion,methyl
demeton and Ethyl parantrophenyl phenylphosphorothroate, EPN only)
(mg/l)
1.0
Polychlorinated biphenyls, PCBs (mg/l) 0.003
pH ( Hydrogen ion activity----marine) 5.0-9.0
pH ( Hydrogen ion activity--non marine) 6.5-8.5
Phenols (mg/l) 0.001
Selenium (mg/l) 0.01
Selenium and its compounds (mg/l) 0.1
Hexavalent Chromium VI compounds (mg/l) 0.5
Sulphide (mg/l) 0.1
Simazine (mg/l) 0.03
Total Suspended Solids, (mg/l) 30
Tetrachloroethylene (mg/l) 0.1
Thiobencarb (mg/l) 0.1
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Temperature (in degrees celious) based on ambient temperature ± 3
Thiram (mg/l) 0.06
Total coliforms ( counts /100 ml) 30
Total Cyanogen (mg/l) Nd
Total Nickel (mg/l) 0.3
Total Dissolved solids (mg/l) 1200
Colour in Hazen Units (H.U) 15
Detergents (mg/l) Nil
Total mercury (mg/l) 0.005
Trichloroethylene (mg/l) 0.3
Zinc (mg/l) 0.5
Whole effluent toxicity
Total Phosphorus (mg/l) 2 Guideline value
Total Nitrogen 2 Guideline value
And any other parameters as may be prescribed by the Authority from time to time
Remarks
Standard values are daily/monthly average discharge values. Not detectable (nd) means that
the pollution status is below the detectable level by the measurement methods established by
the Authority.
2.9.2 OFFENCES
Contravening the above regulations constitutes an offence.
As outlined in PART VI MISCELLANEOUS PROVISIONS of the NEMA WATER
QUALITY REGULATIONS
Offences 27. (1) Any person who contravenes any of these Regulations commits
an offence and shall be liable on conviction to a fine not exceeding five
hundred thousand shillings.
(2) In addition to the above, the court may give such other orders as
provided for by the Act.
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3 METHODOLOGY
3.1 INTRODUCTION
The aim of this study was to determine the quality of grey water and the application of
internal waste treatment systems. In remote areas, we find that there is mostly a lack of an
operational sewer system. Therefore, households have to establish on-site waste management
methods. Such methods include, septic tanks, soil percolation systems and pit latrines.
3.2 BACKGROUND KNOWLEDGE OF THE STUDY AREA
Samples were collected from a block of residential flats in Ongata Rongai.
MAP 1: THE SATELLITE IMAGE OF THE AREA OF STUDY
Plate 3.1 Sampling point: Block of apartments
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3.2.1 LOCATION
Ongata-Rongai is a fast developing residential urban aggregation within Kajiado County;
situated at Kajiado’s border Nairobi at latitude (0° -53' 60 S), and longitude (36° 25' 60E).
Located 50 Kilometres from Kajiado District Headquarters (the core to which it is
subordinate), and 20 Kilometres from Nairobi City Centre on the Langata-Magadi Road,
several reasons explain the growth of this area which started in the late 1950's as a stone
mining township in present day Kware (quarry) area of Rongai.
3.2.2 PLANNING AND URBAN DEVELOPMENT
As a local satellite urban centre, it owes its existence to proximity to Nairobi (locational
advantage). Secondly, Ongata Rongai grew out of a small settlement put up by casual
labourers who provided labour to neighbouring affluent Karen.
Ongata Rongai functions as Nairobi’s dormitory. Physical development in the area has not
occurred under planning control, with haphazard developments first coming along Magadi
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road and then spreading into the interior. Present too, is unchecked animal keeping and
settlements polluting Mbagathi River.
Dominated by economic motive and in total disregard of social, aesthetic and environmental
long-term impacts on the areas’ inhabitants; private developers dictate pace of physical
developments. This has resulted in high densities, overcrowded housing, unsanitary
conditions, diminishing open spaces, and haphazard peripheral development.
This is precipitated by increasing demand for shelter, physical and social infrastructure,
ineffective physical planning systems, informal investment finance and speculative land
costs.
3.2.3 GEOGRAPHY AND ECONOMY
Ongata Rongai with two administrative wards; Ongata-Rongai and Nkaimurunya, has mixed
population except for lacking upper class in socio-economic terms.
Ongata Rongai spatially consists of four areas namely Rongai shopping centre, a commercial
area to the north, Nkoroi, an upper class area to the south, Kandisi, a semi-rural area to the
east and Kware, a slum to the west. Though predominantly residential, formal and informal
commercial developments have come up in an unplanned fashion, and functionally zoning
the area along Magadi road.
3.2.4 INFRASTRUCTURE
Though characterised by proliferation of road links to Nairobi, Ngong and Kiserian to enable
commuter travel, Rongai lacks infrastructure and social amenities commensurate to its
population. An example is the acute shortage of public schools. Rongai’s single bitumen
standard Magadi road serves its entire population, while local access roads are narrow and
un-tarmacked.
Ongata Rongai lacks a trunk sewer. 53 per cent of residents rely on septic/ conservancy tanks
whereas 43 per cent use pit latrines. Oloolaier Water and Sewage Company operated a
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sewage exhauster which has since been grounded. Residents contract private solid waste
disposal companies.
The main challenges for water and sewerage provision are:
1. Narrow roads in private land leaving no room for laying of water and sewer pipes.
2. Lack of land for sewerage treatment.
3. Limited financing for water and sewage connections.
3.2.5 SAMPLING POINT
The sampling point was 2 blocks of residential flats namely “Gits” and “Josally” that lead its
wastewater to a similar central point.
Collectively, these two blocks of flats had a population of approximately 74 residents.
3.3 METHOD OF STUDY
3.3.1 SAMPLING
As in the case of wastewater, the value of wastewater analyses depends largely upon the
accuracy of sampling. Thus it was necessary to observe strict precautions in the selection of
sampling points and methods of sampling to ensure the collection of representative samples
at all times.
At the block of flats, grey water is separated from black water. Black water is led to an
underground septic tank within the compound of the block of flats. Grey water on the other
hand, is led to an access manhole which further leads the wastewater to a soil percolation
system where the grey water percolates into the soil.
3.3.1.1 OBTAINING SAMPLE 1
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This was obtained directly from the manhole.
Plate 3-2: Access Manhole, sampling point 1.
From the PHE Laboratory at Hyslop building, 2 sampling bottles were obtained.
One 500ml plastic bottle and a 250ml glass bottle. Using these bottles, the samples of grey
water were obtained by simply submerging the bottles into the access manhole until they
were completely full.
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Plate 3-3: Obtaining the sample 1 a)
Plate 3-4: Obtaining the sample 1 b)
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Plate 3-5: The sample 1 collected.
3.3.1.2 OBTAINING SAMPLE 2
This was obtained directly from the pipe.
From the PHE Laboratory at Hyslop building, 2 sampling bottles were obtained.
One 500ml plastic bottle and a 250ml glass bottle. Using these bottles, the samples of grey
water were obtained by filling the bottles with grey water flowing from the pipe until they
were completely full
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Plate 3-6: Pipe, sampling point 2.
Plate 3-7: The sample 2 collected.
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Care was taken not to disturb the contents by creating currents at the sampling point.
Examination of the samples should ideally be made as soon as possible after collection.
3.3.2 LABORATORY TESTS.
Laboratory tests were conducted after sampling in the Public Health Engineering Laboratory
at the University of Nairobi.
The tests performed were:
• Faecal bacteria
• General coliform
• pH
• BOD (Biochemical Oxygen Demand)
• COD (Chemical Oxygen Demand)
• Dissolved oxygen
• Chloride
• Solids: Suspended
• Sulphates.
Plate 3-8: PHE Laboratory.
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3.3.2.1 LAB PROCEDURES.
a) pH
Method (pH meter)
About 75ml of the sample was placed in a 100 ml beaker. The electrodes were carefully
raised out of the beaker and rinsed with distilled water. Drops of water from the electrodes
were wiped. The electrodes were then immersed in the beaker containing the sample.
The selector switch was turned to ‘pH’. The pH was read directly from the meter and
recorded. The selector switch was then turned to “CHECK”.
Carefully, the electrodes were raised and rinsed with distilled water. They were then replaced
into the beaker of distilled water.
b) Chloride
Method
To 100 ml of the sample, 1 ml of potassium chromate solution was added in a conical flask.
The mixture was then titrated against standard silver nitrate solution with constant stirring
until a slight red precipitate appears.
The volume if titrant used is recorded and concentration of chloride calculated.
c) Dissolved Oxygen (DO)
Reagents
- Manganous Sulphate solution
- Concentrated Sulphuric acid
- Starch indicator solution
- Alkali-azide-iodide reagent
- Standard Sodium Thiosulphate Solution, 0.025N
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Method
The sample was poured into a DO bottle until full. The volume of the DO bottle was 280ml.
The stopper was replaced carefully so as not to trap any air bubble in the bottle. The stopper
was then removed and in quick succession, 2ml of Manganous Sulphate Solution and Alkali-
azide-iodide reagent were added with the tip of the pipette well below the water level in the
bottle.
The sample did not turn yellow on adding the reagents hence concluded that the DO in the
sample is too little. (Below 1.0mg/l).
d) General Coliform
Presumptive Test
Reagents and Apparatus
- Durham tubes
- MacConkey broth media
- Incubator
- Fermentation tubes
Method
Untreated water from raw water sources (as was my case) were examined using different
inoculation volumes in tenfold dilution steps. The following inoculations were prepared.
10ml of sample to each of three tubes containing 10 ml of double-strength medium;
1.0 ml of sample to each of three tubes containing 10 ml of single-strength medium;
1.0 ml of a 1: 10 dilution of sample (i.e. 0.1 ml of sample) to each of three tubes
containing 10 ml of single-strength medium.
In each fermentation tube, there was an inverted Durham tube. This tube was to be filled with
the sample. The purpose of these tubes were to catch any gas produced. This method was
enhanced by using indicator medium which changes colour when acid forming species are
present. In my case, colour change was from purple to cloudy yellow for the first
presumptive test.
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After gently shaking the tubes to mix the contents, the tubes were incubated at a temperature
of 37℃ for 48 hours. However, observations were made after 24 hours to check for positive
indications of coliform. Incubation began at 1: 55 pm.
After 24 hours, the samples from presumptive tests were observed for the presence of gas.
Using a loop wire, broth was transferred from the passed presumptive test fermentation tube
into a corresponding confirmative test fermentation tube.
For the tubes from the presumptive test that had negative results i.e. no presence of gas in the
Durham tube, they were re-incubated for a further 24 hours at the same temperature of 37℃.
After 48 hours, the presumptive test samples that had not passed were observed to check the
presence of gas in the inverted Durham tubes. The samples that were positive i.e. presence of
gas in the inverted Durham tubes, were transferred using a wire loop into the corresponding
confirmatory test fermentation tube.
The presumptive test sample that was negative after 48 hours was discarded.
Confirmatory Test
Reagents and Apparatus
- Durham tubes
- Incubator
- Fermentation tubes
- Brilliant green lactose (bile) broth.
Method
Similar to the presumptive test, the following media were prepared;
Three tubes containing 10 ml of double-strength medium;
Three tubes containing 10 ml of single-strength medium;
Three tubes containing 10 ml of single-strength medium.
The confirmative test fermentation tubes also had inverted Durham tubes which were filled
with the sample.
Only samples that passed the presumptive test were used in the confirmatory test.
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They were then incubated at 37℃ for 48 hours.
After 24 hours, observations were made to check for the presence of gas in the inverted
Durham tubes and the results recorded.
The samples that were negative i.e. no presence of gas in the inverted Durham tubes were re-
incubated for an additional 24 hours at the same temperature of 37℃.
After 48 hours, the remaining confirmatory test samples were observed for the presence of
gas in the inverted Durham tubes.
Statistical tables were then used to derive the concentration of general coliforms in the
sample.
e) Faecal Bacteria (E. coli)
Reagents and Apparatus
- Durham tubes
- Incubator
- Fermentation tubes
- Brilliant green lactose (bile) broth.
Method
Similar to the confirmatory test, the following media were prepared;
Three tubes containing 10 ml of double-strength medium;
Three tubes containing 10 ml of single-strength medium;
Three tubes containing 10 ml of single-strength medium.
The E. coli test fermentation tubes had inverted Durham tubes.
Samples from the confirmatory that were positive for general coliform were used in this test.
Using a wire loop, samples from positive confirmatory sample, were transferred into
corresponding the E. coli fermentation tubes.
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The Durham tubes were filled with the sample. The samples were then incubated at 44℃ for
48 hours.
After the full 48 hours, the samples were observed and those that were positive were recorded
whereas the negative ones were discarded.
Statistical tables were then used to derive the concentration of faecal coliforms (E. coli) in the
sample.
f) Chemical Oxygen Demand (COD)
Reagents and Apparatus
- Distilled water
- Standard Potassium dichromate solution (0.025N)
- Concentrated Sulphuric acid containing silver sulphate
- Standard ferrous ammonium sulphate (0.1N)
- Powdered mercuric sulphate
- Phenanthroline ferrous sulphate (ferroin indicator solution)
- Reflux apparatus with ground glass joint
- 250ml Erlenmeyer flask with ground glass joint
- Glass beads
- Pipettes
Method
To a 250ml Erlenmeyer flask, the following was added;
0.4 g solid mercuric sulphate
0.5 ml of the sample
10.0 ml of 0.25 N potassium dichromate
A few glass beads
The above was repeated but with 20.0 ml of distilled water instead of the sample to act as
blank. The flask was fitted to the condenser system, making sure the ground glass joint was
snug. The flow of cooling water was started through the condensers.
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Very slowly, 30 ml of silver sulphate-concentrated sulphuric acid solution was added to the
flask through the open end of the condenser. The contents of the flask were mixed by
swirling while adding the acid.
The heaters were switched on and the flasks refluxed for two hours. The heaters were then
switched off. The condensers were rinsed with distilled water and the flask removed from the
heater after disconnecting the condenser, carefully after they cooled.
The contents of each flask were then diluted with distilled water to about 150 ml, mixing the
contents while adding the distilled water.
2-3 drops of Ferroin indicator were added to each flask. The contents of the flask were
titrated with standard ferrous ammonium sulphate solution of 0.1 N strength.
The end point of the experiment was a colour change from blue-green to reddish brown. The
volume of the titrant used was observed and recorded.
COD of the sample was then determined through the following formula
(Mg/l) COD = (𝑎−𝑏 ) ×𝑁 ×8000
𝑚𝑙 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒
Where a = ml of titrant used for the blank
b = ml of titrant used for the sample
N = normality of the sample (0.1N)
g) Biochemical Oxygen Demand
Reagents and Apparatus
Reagents for Dilution water: 1. Phosphate Buffer solution
2. Ferric Chloride solution
3. Magnesium sulphate solution
4. Calcium chloride solution
5. Manganous sulphate solution
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6. Concentrated Sulphuric Acid
7. Starch indicator solution
8. Standard sodium Thiosulphate solution 0.025N
Apparatus
- Burettes
- Pipettes
- BOD bottles
Method
6 litres of dilution water was prepared by adding
- 6 ml of phosphate buffer solution
- 6 ml of ferric chloride solution
- 6 ml of magnesium sulphate solution
- And 6 ml of calcium chloride solution,
To 6 litres of distilled water kept aerated in the aspirator bottle. They were mixed well and
aeration continued. The BOD bottles to be used had a capacity of 300 ml each. The volume
of sample to be taken in each bottle was calculated which when filled with dilution water will
result in dilutions of 1:300, 1:560, 1:750, 1:1000 and 1: 1500.
The five sets of BOD bottles each set containing two bottles were arranged. The bottles were
then labelled with the dilution factors mentioned above. The calculated amounts of sample
was transferred to each bottle as appropriate.
The bottles were then filled with dilution water without overflowing and the stopper replaced
without trapping any air bubble. Another set of two bottles was taken. They were identified
as dilution water BLANK and they were filled with dilution water without any sample.
The dissolved oxygen concentration in one bottle was determined from each of the six sets of
bottles as follows.
The stopper was removed and in quick succession, 2 ml each of manganous sulphate solution
and alkali azide-iodide reagent with the tip of the pipette well below the water level in the
bottle was added. The stopper was replaced again taking care not to trap any air bubbles.
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The contents of the bottle were mixed by inverting the bottle several times and letting the
precipitate settle half-way down the bottle. The contents were mixed again and the precipitate
let to settle again as before
2 ml of concentrated sulphuric acid was added to the contents of the bottle using a bulb, with
the tip of the pipette just below the water level. The stopper was replaced and the contents
mixed again, till all the precipitate dissolved.
203 ml was measured from the bottle and transferred to an erlenmeyer flask. This was then
titrated against standard sodium thiosulphate solution till all the colour changed to pale
yellow. 1 ml of starch indicator solution was added and titration continued until all the blue
colour disappeared. Reappearance of the blue colour after the first disappearance was
disregarded.
The remaining bottle in each of the six sets were incubated at 20℃ for 5 days in the incubator
cabinet.
Once 5 days were over, the DO was determined for each dilution as stated above. Volume of
titrant used was observed and recorded. The DO was then determined using the following
formula.
DO, mg/l = ml of titrant used under above conditions
h) Suspended solids
Apparatus
- Filter paper
- Desiccator
- Drying oven
- Suction pump
Procedure
The weight of a new filter paper was determined using an analytical balance (W1). The filter
paper was then mounted onto the suction pump. The sample was shaken vigorously and 20
ml transferred rapidly to the funnel of the suction pump by means of a 100ml volumetric
cylinder.
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The suction pump was then turned on and was left to run until all the sample had passed
through the filter paper. The filter paper was then removed carefully and dried in the oven to
constant weight i.e. overnight.
The filter paper and contents were then weighed (W2).
TSS in mg/l = 𝑊2−𝑊1
𝑚𝑙 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 𝑓𝑖𝑙𝑡𝑒𝑟𝑒𝑑
TSS = Total Suspended Solids
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4 RESULTS AND ANALYSIS
4.1 1ST SAMPLE (FROM MANHOLE)
4.1.1 LAB RESULTS
a. PH
PH meter reading: 6.59
b. Chloride
Initial reading: 0.0 ml
Final reading: 38.4 ml
Volume used: 38.4 ml
Chloride concentration = 38.4 × 10
Chloride concentration = 384 mg/l
c. Dissolved Oxygen
D.O below than 1.0 mg/l
D.O concentration = <1.0mg/l
d. General Coliforms
Final result.
Positive result: Presence of air bubble in the inverted Durham tube after incubation at 37℃
for 48 hours.
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Table 4.1: GENERAL COLIFORMS LAB RESULTS
Double strength
(10ml sample)
Single strength
(1ml of sample)
Single strength
(0.1 ml of sample)
3 3 2
Therefore, 1100 coliforms per 100ml of sample.
From table 908.11 Standard Methods for Examination of Waste and Wastewater 14th
Edition
1975
e. Faecal Bacteria (E. coli)
Final result.
Positive result: Presence of air bubble in the inverted Durham tube after incubation at 44℃
for 48 hours.
Table 4.2: E. COLI LAB RESULTS
Double strength
(10ml sample)
Single strength
(1ml of sample)
Single strength
(0.1 ml of sample)
2 0 2
Therefore: 14 E. coli in 100 ml of sample
From table 908.11 Standard Methods for Examination of Waste and Wastewater 14th
Edition
1975
f. COD
0.5 ml of sample was used in this test.
Table 4.3: COD LAB RESULTS
Reagent Initial Final Volume of titrant
Blank 0.0 24.0 24.0
Sample 0.0 20.1 20.1
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(Mg/l) COD = (24.0−20.1 ) ×0.1 ×8000
0.5
COD = 6560 mg/l
g. BOD
This sample was quite polluted, hence 6 sets of BOD bottles were prepared in the
following ratios. BOD bottles used had a volume of 300ml.
1:560 (0.5ml)
1:750 (0.4ml)
1:1000 (0.3ml)
1:1500 (0.2ml)
1:300 (1ml)
Blank
Table 4.4: BOD0
Ratio Initial Reading Final Reading Volume of Titrant
1: 1500 7.0 14.4 7.4
1:1000 14.4 21.8 7.4
1:750 21.8 29.1 7.3
1:560 29.1 36.3 7.2
1:300 0.0 7.0 7.0
Blank 36.3 43.9 7.6
Table 4.5: BOD5
Ratio Initial Reading Final Reading Volume of Titrant
1: 1500 10.9 14.9 4.7
1:1000 7.6 10.9 3.3
1:750 2.4 4.0 2.0
1:560 1.0 2.4 0.5
1:300* NO OXYGEN
Blank 0.0 7.6 7.6
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1:300 sample did not have any dissolved oxygen remaining. This was because, on addition of
2 ml each of manganous sulphate solution and alkali azide-iodide reagent, the sample turned
white signifying no oxygen remaining. The test ended there for that particular sample.
Table 4.6: CALCULATION OF BOD
Ratio BOD0-Vol (V1) BOD5-Vol (V2) V1 – V2 BOD 5
1: 1500 7.4 4.7 2.7 3.4*1500 = 4050
1:1000 7.4 3.3 4.1 4.1*1000 = 4100
1:750 7.3 2.0 5.3 5.3*750 = 3975
1:560 7.2 0.5 6.7 6.7*560=3752
1:300* 7.0 NO OXYGEN -
Average BOD5 values
BOD5 = 4050+4100+3975+3752
4
BOD5 = 3969.3 mg/l
Plate 4-1: Sample 1:300 fully depleted of Dissolved Oxygen
4.2 2ND SAMPLE (FROM PIPE)
4.2.1 LAB RESULTS
a. PH
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PH meter reading: 7.56
b. Chloride
Initial reading: 15.3 ml
Final reading: 37.9 ml
Volume used: 22.6 ml
Chloride mg/l = 22.6 × 10
Chloride = 226 mg/l
c. Dissolved Oxygen
Initial reading: 42.8 ml
Final reading: 43.3 ml
Volume used: 0.5 ml
DO concentration = 0.5 mg/l
d. Sulphates
Sample turbidity: 100
Sulphates concentration = Above 500 mg/l
e. Suspended solids
20 ml of sample.
Weight of filter paper: 0.168g
Filter paper and suspended solids: 0.179g
TSS in mg/l: 0.179 – 0.168
20 = 0.00055 mg/l
Suspended solids = 0.00055 mg/l
f. General Coliforms
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Final result.
Positive result: Presence of air bubble in the inverted Durham tube after incubation at 37℃
for 48 hours.
Table 4.7: GENERAL COLIFORMS LAB RESULTS
Double strength
(10ml sample)
Single strength
(1ml of sample)
Single strength
(0.1 ml of sample)
3 3 1
Therefore, 460 coliforms per 100ml of sample.
From table 908.11 Standard Methods for Examination of Waste and Wastewater 14th
Edition
1975
g. Faecal Bacteria (E. coli)
Final result.
Negative result: No air bubble in the inverted Durham tube after incubation at 44℃ for 48
hours.
Table 4.8: E. COLI LAB RESULTS
Double strength
(10ml sample)
Single strength
(1ml of sample)
Single strength
(0.1 ml of sample)
0 0 0
Therefore: No E. coli
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From table 908.11 Standard Methods for Examination of Waste and Wastewater 14th
Edition
1975
h. COD
2 samples were used in this test
5 ml sample
2 ml sample
Table 4.9: COD LAB RESULTS
Reagent Initial Final Volume of titrant
Blank 0.0 24.7 24.7
5 ml Sample 23.5 45.2 21.7
2 ml sample 0.0 23.5 23.5
Calculation
5ml: COD
(24.7 – 21.7) × 8000 × 0.1
5 = 480 mg/l
2ml: COD
(24.7 – 23.5) × 8000 × 0.1
2 = 480 mg/l
Average COD values
480 + 480
2 = 480
COD = 480 mg/l
i. BOD
This sample was not as polluted, hence 4 sets of BOD bottles were prepared in the following
ratios. BOD bottles used had a volume of 280ml.
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1:50 (5.6ml)
1:100 (2.8ml)
1:200 (1.4ml)
Blank
Table 4.10: BOD0
Ratio Initial Reading Final Reading Volume of Titrant
1: 50 7.3 14.5 7.2
1:100 14.5 21.7 7.2
1:200 22.3 29.6 7.3
Blank 0.0 7.3 7.3
Table 4.11: BOD5
Ratio Initial Reading Final Reading Volume of Titrant
1: 50 6.8 8.0 1.2
1:100 8.0 12.4 4.4
1:200 12.4 18.1 5.7
Blank 0.0 6.8 6.8
Table 4.12: CALCULATION OF BOD
Ratio BOD0-Vol (V1) BOD5-Vol (V2) V1 – V2 BOD 5
1: 50 7.2 1.2 6.0 6.0*50 = 300
1:100 7.2 4.4 2.8 2.8*100 = 280
1:200 7.3 5.7 1.6 1.6*200 = 320
Average BOD values
300 + 280 + 320
3 = 300
BOD5 = 300 mg/l
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5 DISCUSSIONS
5.1 LAB RESULTS
Table 5.1: LAB RESULTS
Parameter Sample 1 Sample 2
Total Suspended Solids 2100 550
Sulphates >500 500
Chloride 384 226
BOD 3969.3 300
COD 6560 480
pH 6.59 7.56
Faecal bacteria (E. coli) 14 Nil
Total coliforms 1100 460
5.1.1 SAMPLE 1 (FROM MANHOLE)
This sample was highly polluted. Most surprisingly, it contained E. coli which does not
reflect the fact that grey water originates from kitchens and bathrooms hence ideally, should
not contain E. coli.
In addition, the COD and BOD values were far too large. This was because, the sampling
point contained grey water that had been stagnant for an unknown period.
Stagnant grey water is susceptible to contamination and will in time become septic. This
explains the highly polluted sample.
5.1.2 SAMPLE 2 (FROM PIPE)
This sample was obtained from the water flowing from the pipe into the access manhole. It
had a better representation of the study objectives as observed from the laboratory test results.
The results obtained were acceptable and much lower than the results from the initial
manhole sample.
Errors encountered were small and acceptable. Such experimental errors may have risen from
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- Contamination of sampling equipment when obtaining the sample.
- Contamination of the sampling point from external factors.
- Parallax error in reading volumes of reagents in the laboratory.
5.2 POLLUTION LEVELS OF SAMPLES
Results of the samples tested versus the set standards can be tabulated as shown below
Table 5.2: COMPARISON OF SAMPLE POLLUTION LEVELS AGAINST WQ
REGULATIONS
Parameter Sample 1 Sample 2 WQ standard
Total Suspended Solids 2100 550 30
Sulphates >500 500 -
Chloride 384 226 250
BOD 3969.3 300 30
COD 6560 480 250
pH 6.59 7.56 6.5 – 8.5
Faecal bacteria (E. coli) 14 Nil Nil
Total coliforms 1100 460 30
5.3 REMARKS ON POLLUTION LEVELS
5.3.1 SAMPLE 1
As earlier indicated, Sample 1 was much polluted and as seen from Table 5.2. The only
parameter that conformed to the WQ regulations was pH. The other parameters exceeded the
WQ regulations by much.
The high levels of pollution can be attributed to the fact that this water was stagnant hence
turning septic.
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5.3.2 SAMPLE 2
Parameters that conformed to the WQ regulations include:
- Chloride
- Faecal bacteria
- pH
This as compared to Sample 1 proved to be less polluted. However, some important
parameters such as BOD and COD were too far exceeded.
Of significance was that, Sample 2 did not have faecal bacteria meaning that there was no
cross-contamination with black water. Presence of E. coli in grey water will indicate cross-
contamination with black water (waste water from toilets) and hence the piping system will
need repair.
5.4 HOW TO HANDLE GREY WATER
5.4.1 DIVERT TO SEPTIC TANK
Conventional practise has been to direct all wastewater to a septic tank which is then emptied
from time to time of sludge using a tanker with a suction pump.
This practise has some shortcomings as listed below;
- For homeowners, more waste water volumes being directed to the septic translates to
added running and maintenance costs for the septic tanks.
- Directing grey water to septic tanks greatly increases the load carried by the septic
system leach field, hence reducing the system’s life expectancy and effectiveness.
- Grey water is laden with phosphates from soaps and detergents such that when
directed to the septic, it ends up disrupting the digestive function of the septic tank.
As observed above, this measure is not as effective.
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5.4.2 FILTRATION AND SETTLING SYSTEM
5.4.2.1 SCREEN
Screen can be a mesh with less than 10 mm size to remove coarse particles. The screens can
be placed at the inlet to the piping system of sources such as bathroom, sinks etc. to remove
large particles and prevent an overload of particles at the outlet.
The screens can be cleaned manually and solids disposed along with solid waste.
5.4.2.2 USE OF SETTLING TANK
Use of a settling tank enables solids and large particles to settle to the bottom, while grease,
oils and small particles will float.
Such tanks should be large enough to hold twice the expected dally flow plus 40 % to allow
for sludge accumulation and surge loading. One widely-used type of settling tank well-suited
for grey water treatment is a septic tank.
A septic tank is specifically designed to allow settling. The use of a septic tank to treat grey
water should never be confused with the conventional use of a septic tank. Grey water
intended for reuse should never be mixed with toilet wastes.
An electrical pump or aerator could be added to a septic tank to create an aerobic
environment. Using a settling tank prior to discharging waste into the environment will
reduce the pollution loading of the grey water.
Grey water quality will improving by reducing quantity of TSS and with the installation of an
aerator, BOD and COD will also decrease.
5.4.3 USE OF SOAK PIT
This is a covered, porous walled chamber that allows water to slowly soak into the ground.
The grey water is discharged, either raw or from primary treatment, into the underground
chamber from where it infiltrates into the surrounding soil.
As the grey water percolates through the soil from the soak pit, small particles are filtered out
by the soil matrix and organics are digested by microorganisms.
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Soak pits are however very effective for soil with good absorptive properties: clay, hard
packed or rocky soil is not appropriate. Soils with very fast soil percolation rates (i.e., less
than one (1) minute per inch) are not suitable for soak pits. Soils with very fast percolation
rate do not provide adequate treatment of wastewater because the effluent moves too quickly
through the soil and may reach ground water before being fully treated.
Soak pits should not be constructed directly over visible bedrock, cracks, crevices,
depressions, sinkholes or other susceptible geologic formations to protect the underlying
aquifer.
Soak pits should be located a safe distance from a drinking water source especially if the
drinking water is sourced from a shallow well.
Water tables are not static, and may rise above the bottom of the seepage pit, flooding it and
allowing direct contact of pathogens and nitrogen species with ground water.
Soak pits would be most effective if the effluent has undergone some primary treatment.
5.4.4 USE OF WETLANDS
Physical, chemical, and biological processes are combined in wetlands to remove
contaminants from wastewater. Grey water treatment is achieved by soil filtration in reed-bed
systems which reduces the organic load of the grey water considerably
In addition, constructed wetlands decrease the concentration of faecal bacteria. If designed
properly, these systems would produce a clear and odourless effluent.
Constructed wetlands tend to be simple, cheap to maintain and environmentally friendly.
However, construction of wetlands require large amount of space that is not available at the
block of apartments.
5.4.5 DISINFECTION
A little disinfection before discharging effluent into the environment helps to reduce the
pollution levels.
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An appropriate chemical to be used to disinfect water is chlorine. This is because it is cheap,
readily available, and stable and will, with time, vaporize from the water after disinfection.
Organic matter in grey water may combine with chlorine hence reducing the amount
available for the disinfection process. Because of this reason, a settling tank or filter before
this stage is highly recommended.
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6 CONCLUSION
From the findings, it is clear that the grey water effluent exceeds the WQ regulations for effluent
discharged into the environment. Hence therefore, this effluent should undergo primary treatment
before discharge into the environment.
The other option should thus be discharge into the septic tank for non-sewered areas or discharge
into the public sewer for sewered areas.
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7 RECOMMENDATIONS
- Residents in rural areas should partner with the county government to set up a public
sewer system to avoid rampant effluent discharge which may be hard for enforcing
bodies like NEMA to monitor.
- For residents with enough space, wetlands are effective, cheap and easy to install for
treating grey water. Effective wetlands can even produce water that can be reused for
irrigation and other commercial purposes. This water cannot be used for drinking.
- Well designed soak pits are effective but disinfection and settling tanks systems prior
to this ensures that soak pits are effective.
- Enforcing bodies like NEMA should carry out regular quality assessment of effluent
discharged into the environment to ensure that the set standards are not exceeded.
This project can be used and modified so as to provide a solution to grey water treatment and
discharge in non-sewered areas.
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8 REFERENCES
A-Boal, D. Christov, Lechte, P. and Shipton, R. 1995. Installation and Evaluation of
Domestic grey water reuse Systems: Executive Summary. Department of Civil and Building
Engineering, Victoria University of Technology, Victoria, Australia: Victoria University of
technology, 1995. Technical Memorandum
Environmental Management and Coordination, (Water Quality) Regulations 2006:
Environmental Management and Coordination Act, (1999), the Minister for Environment and
Natural Resources
Guidelines for drinking-water quality. 2nd
Edition: Volume 3 Surveillance and control of
community supplies. World Health Organization, Geneva 1997.
Little, V. 2000: Residential grey water reuse: The Good, The Bad, The healthy. Tucson, AZ:
The Water Conservation Alliance of southern Arizona (Water CASA), 2009
Mullegger E, Langergrabber G. Jung H. Starkl M. and Laber J. 2003: Potential for Grey
water treatment and reuse in rural areas, 2nd
International Symposium on ecological sanitation
Peter L.M. Veneman and Bonnie Stewart 2002: Grey water characterization And
Treatment Efficiency; Final Report for The Massachusetts Department of Environmental
Protection, Bureau of Resource Protection, December 2002
Public Health Engineering Laboratory Manual: Department of Civil Engineering,
University of Nairobi.
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APPENDIX
PHOTO GALLERY
Plate 8-1: Presumptive Test Reagents
Plate 8-2: BOD Test Bottles
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Plate 8-3: Positive Presumptive Test Results
Plate 8-4: PH Meter